PUERTO PRINCESA, Philippines, May 21 (Reuters) - Nine Chinese fishermen pleaded not guilty on Wednesday before an environment court in the Philippines after they were caught with hundreds of marine turtles in a disputed shoal in the South China Sea.

A boat unit of the Philippine National Police intercepted the Chinese fishing boat and arrested its 11 crew members this month in Half Moon shoal in the disputed Spratly islands.

If convicted of illegal fishing and violating the U.N. Convention on trading of endangered species, the men face prison terms of 12 to 20 years. They were granted permission to post bail of of 70,000 pesos ($1,600) each pending further sittings.

A court-appointed defence lawyer entered a not guilty plea for the men, who stood silently while the charges were read out in a court in Puerto Princesa on the island of Palawan in the west of the Philippine archipelago. The judge set a pre-trial hearing for June 4.

“They agreed to participate in the trial and took the services of the public attorney’s office as their counsel,” Allen Ross Rodriguez, Palawan’s provincial prosecutor, told reporters. The fishermen, he said, had initially declined to take part in the proceedings.

Two fishermen were freed and sent home to southern China after authorities determined they were minors.

Philippine prosecutors rejected demands from Beijing to free the men on grounds they were arrested in Chinese waters. About 350 marine turtles were seized from their boat, about 100 km (60 miles) west of Palawan.

China lays claim to almost all the South China Sea, believed to be rich in energy and fisheries resources. Brunei, Malaysia, the Philippines, Vietnam and Taiwan also claim parts of the sea.

President Benigno Aquino this week accused China of violating an informal code of conduct in the South China Sea with land reclamation work in another disputed shoal.